Fulminant hepatocyte apoptosis in vivo following microcystin-LR administration to rats

Cyanotoxins in African waterbodies: occurrence, adverse effects, and potential risk to animal and human health

Public concerns about cyanotoxins production in water and its detrimental impacts on human and animal health are growing primarily due to the widespread eutrophication observed in aquatic ecosystems. A review of relevant literature was done to determine the degree of cyanotoxin occurrence and its harmful effects in African waterbodies. Data were extracted from 64 published studies from 1990 to 2022 that quantified the concentration of cyanotoxins in African aquatic ecosystems. Cyanotoxins have been reported in 95 waterbodies (29 lakes, 41 reservoirs, 10 ponds, 9 rivers, 5 coastal waters, and 1 irrigation canal) from 15 African countries. Cyanotoxins were documented in all the regions of Africa except the central region. Microcystins have been reported in nearly all waterbodies (98.9%), but anatoxin-a (5.3%), cylindrospermopsin (2.1%), nodularins (2.1%), homoanatoxin-a (1.1%), and β-N-methylamino-L-alanine (1.1%) were encountered in a small number of water ecosystems, homoanatoxin-a and β-N-methylamino-L-alanine each occurred in one waterbody. The largest concentrations of microcystins and nodularins were reported in South African Lakes Nhlanganzwani (49,410 μg L-1) and Zeekoevlei (347,000 μg g-1). Microcystin concentrations exceeding the WHO guideline for lifetime drinking water (1 μg L-1) were reported in 63% of the aquatic ecosystems surveyed. The most frequently reported toxin-producing cyanobacteria genus is Microcystis spp. (73.7%), followed by Oscillatoria spp. (35.8%) and Dolichospermum spp. (33.7%). Cyanotoxin-related animal mortality and human illness were reported in the continent. Consequently, it is necessary to regularly monitor the level of nutrients, cyanobacteria, and cyanotoxins in African waterbodies in an integrated manner to devise a sustainable water resources management.

LC-MS/MS Validation and Quantification of Cyanotoxins in Algal Food Supplements from the Belgium Market and Their Molecular Origins

Food supplements are gaining popularity worldwide. However, harmful natural compounds can contaminate these products. In the case of algae-based products, the presence of toxin-producing cyanobacteria may cause health risks. However, data about the prevalence of algal food supplements on the Belgian market and possible contaminations with cyanotoxins are scarce. Therefore, we optimized and validated a method based on Ultra High Performance Liquid Chromatography-Tandem Mass Spectrometry to quantify eight microcystin congeners and nodularin in algal food supplements. Our analytical method was successfully validated and applied on 35 food supplement samples. Nine out of these samples contained microcystin congeners, of which three exceeded 1 µg g−1, a previously proposed guideline value. Additionally, the mcyE gene was amplified and sequenced in ten products to identify the taxon responsible for the toxin production. For seven out of these ten samples, the mcyE gene could be amplified and associated to Microcystis sp. EFSA and posology consumption data for algal-based food supplements were both combined with our toxin prevalence data to establish different toxin exposure scenarios to assess health risks and propose new guideline values.

Microcystin-LR exposure results in aberrant spindles and induces apoptosis in porcine oocytes

Microcystin-LR (MC-LR), as a well-known hepatotoxin, was recently found to accumulate in gonads and induce a variety of reproductive damages in zebrafish, mice and other model organisms, however, little information is available on whether MC-LR has toxic effects on the mammalian oocytes, especially in livestock species. In this study, the effects of MC-LR on meiotic maturation of porcine oocytes were investigated, and the potential mechanism of MC-LR toxicity was explored. Germinal vesicle (GV)-stage oocytes were exposed to 0, 20, 40 and 60 μM MC-LR, respectively, during the in vitro maturation for 44 h, and the results showed that the first polar body (PbI) extrusion rate of the oocytes decreased significantly when the MC-LR concentration reached 40 (P < 0.01) or 60 μM (P < 0.001). After treated with 60 μM MC-LR for 44 h, a significant higher percentage of the oocytes arrested at anaphase-telophase I (ATI) stage (P < 0.01). Laser scanning confocal results further confirmed that a significantly larger proportion of the 60 μM MC-LR-treated oocytes exhibited aberrant spindles and misaligned chromosomes, suggesting a failure of spindle assembly and homologous chromosome segregation during the ATI stage. Furthermore, the ROS levels in the 60 μM MC-LR-exposed oocytes were significantly higher than the control group (P < 0.01), while the expression of antioxidant related genes (SOD1, CAT and GPX) were much lower compared with control group, indicating that oxidative stress was induced and the antioxidant capacity of oocytes was depleted by 60 μM MC-LR treatment. Additionally, markedly decreased mitochondrial membrane potential (MMP) (P < 0.01) and significantly higher incidence of early apoptosis (P < 0.01) were observed in the 60 μM MC-LR-treated oocytes, suggesting that MC-LR exposure induced apoptosis in porcine oocytes. Moreover, the protein expression of PP2A was remarkably inhibited, whereas the expression of p53, BAX, Caspase3 and Cleaved-caspase3 were prominently increased in the 60 μM MC-LR-exposed oocytes. Together, these results suggested that 60 μM of MC-LR exposure can induce oxidative stress, and lead to aberrant spindles, impaired MMP, and trigger apoptosis, which eventually result in failure of porcine oocyte maturation.

Short-time Effects of Malathion Pesticide on Functional and Histological Changes of Liver and Kidney in Female Mice

BACKGROUND AND OBJECTIVE

The malathion is one of the most important organophosphorus pesticides used in Iraq. The present study was designed to investigate the short-time effects of the malathion on the biochemical parameters of AST, ALT, ALP, urea, creatinine, total cholesterol, triglycerides and total protein as well as histological changes of the liver and kidneys of female laboratory mice for an interval of 6 days.

MATERIALS AND METHODS

The animals were divided into 3 groups, each group included 8 mice. They were injected with the pesticide in the intraperitoneal region. The 1st group (the control group) was injected with 0.1 mL of distilled water, the 2nd group (the low dose group) was injected with 0.1 mL of the pesticide solution at 3 mg/body weight while the 3rd group (the high dose group) was injected with 0.1 mL of the pesticide solution at a concentration of 6 mg/body weight.

RESULTS

The biochemical tests of the liver and kidney showed significant elevation in serum AST, urea, creatinine and cholesterol concentrations in mice compared to control group (p<0.05). In addition, the results showed a significant decrease in the ALP, triglycerides and the total protein in serum of the treated mice. Also, the results of histological sections of the liver and kidneys included congestion, necrosis, degeneration of cytoplasm, blood congestion, apoptosis, bleeding and sloughing of epithelial cells to the renal tubular lumen.

CONCLUSION

Finally, the results indicated that malathion pesticide has the ability to induce hepatic and renal toxicity in mice within 6 days.

A proteomic study of the pulmonary injury induced by microcystin-LR in mice

MCLR has been shown to act as potent hepatotoxin, and recent studies showed that MCs can accumulate in lung tissue and exert adverse effects. However, the exact mechanism still remain unclear. The present study mainly focuses on the impairments of respiratory system after MCLR exposure in mice. After intratracheal instillation with MCLR (0, 10 and 25 μg/kg bw), histological change was examined in MCLR exposure groups. Results indicated that exposure of MCLR led to serious histopathology alteration and apoptosis in lung of mice. To further our understanding of the toxic effects of MCLR on the lung, we employed a proteomic method to search the mechanisms behind MCLR-induced pulmonary injury. In total, 38 proteins were identified to be significantly altered after MCLR exposure. These proteins involved in inflammatory response, apoptosis, cytoskeleton, and energetic metabolism, suggesting MCLR exerts complex toxic effects contributing to pulmonary injury. Furthermore, MCLR also induced pulmonary inflammation, as manifested by up-regulating the protein levels of interleukin-1β (IL-1β) and p65 subunit. Our results indicated that MCLR exerts lung injury mainly by generating inflammation and apoptosis.

Microcystin-LR induced liver injury in mice and in primary human hepatocytes is caused by oncotic necrosis

Microcystins are a group of toxins produced by freshwater cyanobacteria. Uptake of microcystin-leucine arginine (MC-LR) by organic anion transporting polypeptide 1B2 in hepatocytes results in inhibition of protein phosphatase 1A and 2A, and subsequent cell death. Studies performed in primary rat hepatocytes demonstrate prototypical apoptosis after MC-LR exposure; however, no study has directly tested whether apoptosis is critically involved in vivo in the mouse, or in human hepatocytes. MC-LR (120 μg/kg) was administered to C57BL/6J mice and cell death was evaluated by alanine aminotransferase (ALT) release, caspase-3 activity in the liver, and histology. Mice exposed to MC-LR had increases in plasma ALT values, and hemorrhage in the liver, but no increase in capase-3 activity in the liver. Pre-treatment with the pan-caspase inhibitor z-VAD-fmk failed to protect against cell death measured by ALT, glutathione depletion, or hemorrhage. Administration of MC-LR to primary human hepatocytes resulted in significant toxicity at concentrations between 5 nM and 1 μM. There were no elevated caspase-3 activities and pretreatment with z-VAD-fmk failed to protect against cell death in human hepatocytes. MC-LR treated human hepatocytes stained positive for propidium iodide, indicating membrane instability, a marker of necrosis. Of note, both increases in PI positive cells, and increases in lactate dehydrogenase release, occurred before the onset of complete actin filament collapse. In conclusion, apoptosis does not contribute to MC-LR-induced cell death in the in vivo mouse model or in primary human hepatocytes in vitro. Thus, targeting necrotic cell death mechanisms will be critical for preventing microcystin-induced liver injury.

Eco-epidemiological and pathological features of wildlife mortality events related to cyanobacterial bio-intoxication in the Kruger National Park, South Africa

Over the past decade, several clustered, multispecies, wildlife mortality events occurred in the vicinity of two man-made earthen dams in the southern and south central regions of the Kruger National Park, South Africa. On field investigation, heavy cyanobacterial blooms were visible in these impoundments and analysis of water samples showed the dominance of Microcystis spp. (probably Microcystis aeruginosa). Macroscopic lesions seen at necropsy and histopathological lesions were compatible with a diagnosis of cyanobacterial intoxication. Laboratory toxicity tests and assays also confirmed the presence of significant levels of microcystins in water from the two dams. These outbreaks occurred during the dry autumn and early winter seasons when water levels in these dams were dropping, and a common feature was that all the affected dams were supporting a large number of hippopotamuses (Hippopotamus amphibius). It is hypothesised that hippopotamus' urine and faeces, together with agitation of the sediments, significantly contributed to internal loading of phosphates and nitrogen - leading to eutrophication of the water in these impoundments and subsequent cyanobacterial blooms. A major cause for concern was that a number of white rhinoceros (Ceratotherium simum) were amongst the victims of these bio-intoxication events. This publication discusses the eco-epidemiology and pathology of these clustered mortalities, as well as the management options considered and eventually used to address the problem.

Chlorine/UV Process for Decomposition and Detoxification of Microcystin-LR

Microcystin-LR (MC-LR) is a potent hepatotoxin that is often associated with blooms of cyanobacteria. Experiments were conducted to evaluate the efficiency of the chlorine/UV process for MC-LR decomposition and detoxification. Chlorinated MC-LR was observed to be more photoactive than MC-LR. LC/MS analyses confirmed that the arginine moiety represented an important reaction site within the MC-LR molecule for conditions of chlorination below the chlorine demand of the molecule. Prechlorination activated MC-LR toward UV254 exposure by increasing the product of the molar absorption coefficient and the quantum yield of chloro-MC-LR, relative to the unchlorinated molecule. This mechanism of decay is fundamentally different than the conventional view of chlorine/UV as an advanced oxidation process. A toxicity assay based on human liver cells indicated MC-LR degradation byproducts in the chlorine/UV process possessed less cytotoxicity than those that resulted from chlorination or UV254 irradiation applied separately. MC-LR decomposition and detoxification in this combined process were more effective at pH 8.5 than at pH 7.5 or 6.5. These results suggest that the chlorine/UV process could represent an effective strategy for control of microcystins and their associated toxicity in drinking water supplies.

Hepatic Gene Expression Changes in Mice Associated with Prolonged Sublethal Microcystin Exposure

Microcystin-LR (MCLR) is an acute hepatotoxicant and suspected carcinogen. Previous chronic studies have individually described hepatic morphologic changes, or alterations in the cytoskeleton, cell signaling or redox pathways. The objective of this study was to characterize chronic effects of MCLR in wild-type mice utilizing gene array analysis, morphology, and plasma chemistries. MCLR was given daily for up to 28 days. RNA from the 28-day study was hybridized onto mouse genechip arrays. RNA from 4 hours, 24 hours, 4 days, 1 day, and 28 days for selected genes was processed for quantitative-PCR. Increases in plasma hepatic enzyme activities and decreases in total protein, albumin and glucose concentrations were identified in MCLR-treated groups at 14 and 28 days. Histologically, marked hepatokaryomegaly was identified in the 14-day MCLR group with the addition of giant cells at 28 days. Major gene transcript changes were identified in the actin organization, cell cycle, apoptotic, cellular redox, cell signaling, albumin metabolism, and glucose homeostasis pathways, and the organic anion transport polypeptide system. Using toxicogenomics, we have identified key molecular pathways involved in chronic sublethal MCLR exposure in wild-type mice, genes participating in those critical pathways and related them to cellular and morphologic alterations seen in this and other studies.

The role of GSH in microcystin-induced apoptosis in rat liver: Involvement of oxidative stress and NF-κB

Microcystins (MCs) are potent and specific hepatotoxins produced by cyanobacteria in eutrophic waters, representing a health hazard to animals and humans. The objectives of this study are to determine the relationship between oxidative stress and NF-κB activity in MC-induced apoptosis in rat liver and the role of glutathione (GSH). Sprague-Dawley rats were intraperitoneally (i.p.) injected with microcystin-LR (MC-LR) at 0.25 and 0.5 LD50 with or without pretreatment of buthionine-(S,R)-sulfoximine (BSO), a specific GSH synthesis inhibitor. MC-LR induced time-dependent alterations of GSH levels in rat liver. Increased malondialdehyde (MDA) and significant changes of antioxidant enzymes including GSH peroxidase (GPX) and GSH reductase (GR) were also observed, particularly at 24 h post-exposure. The results indicated that acute exposure to MC-LR induced oxidative stress, and GSH depletion (BSO pretreatment) enhanced the level of oxidative stress. Furthermore, the modulation of pro-apoptotic gene p53 and Bax and anti-apoptotic gene Bcl-2 was observed in 0.5 LD50 group at 24 h, and the alteration was more pronounced by BSO injection before MC-LR treatment, suggesting that GSH played a protective role against MC-induced toxicity. Additionally, electrophoretic mobility shift assay (EMSA) showed that NF-κB was induced at 0.25 LD50 but inhibited at 0.5 LD50 . The above results indicated that the possible crosstalk of oxidative stress and NF-κB activity was associated with MC-LR-induced hepatocytes apoptosis in vivo. Our data will provide a new perspective for understanding the mechanisms of MC-induced liver injury.

Monitoring and removal of cyanobacterial toxins from drinking water by algal-activated carbon

Microcystins (MCs) are the most potent toxins that can be produced by cyanobacteria in drinking water supplies. This study investigated the abundance of toxin-producing algae in 11 drinking water treatment plants (DWTPs). A total of 26 different algal taxa were identified in treated water, from which 12% were blue green, 29% were green, and 59% were diatoms. MC levels maintained strong positive correlations with number of cyanophycean cells in raw and treated water of different DWTPs. Furthermore, the efficiency of various algal-based adsorbent columns used for the removal of these toxins was evaluated. The MCs was adsorbed in the following order: mixed algal-activated carbon (AAC) ≥ individual AAC > mixed algal powder > individual algal powder. The results showed that the AAC had the highest efficient columns capable of removing 100% dissolved MCs from drinking water samples, thereby offering an economically feasible technology for efficient removal and recovery of MCs in DWTPs.

Toxicopathology induced by microcystins and nodularin: a histopathological review

Cyanobacteria are present in all aquatic ecosystems throughout the world. They are able to produce toxic secondary metabolites, and microcystins are those most frequently found. Research has displayed a negative influence of microcystins and closely related nodularin on fish, and various histopathological alterations have been observed in many organs of the exposed fish. The aim of this article is to summarize the present knowledge of the impact of microcystins and nodularin on the histology of fish. The observed negative effects of cyanotoxins indicate that cyanobacteria and their toxins are a relevant medical (due to irritation, acute poisoning, tumor promotion, and carcinogenesis), ecotoxicological, and economic problem that may affect both fish and fish consumers including humans.

Cellular transport of microcystin-LR in rainbow trout (Oncorhynchus mykiss) across the intestinal wall: possible involvement of multidrug resistance-associated proteins

We studied Abcc mediated-transport in middle and posterior intestine of the rainbow trout, Oncorhynchus mykiss. Luminal and serosal transport were evaluated in everted and non-everted intestinal sacs, respectively, incubated with 1-chloro-2,4-dinitrobenzene (CDNB; 200 μM). CDNB enters the cells and is conjugated with glutathione via glutathione S-transferase (GST) to form 2,4-dinitrophenyl-S-glutathione (DNP-SG), a known Abcc substrate. DNP-SG concentration in the bath was recorded every 10 min, in order to calculate the mass-specific transport rate. For evaluating the possible involvement of Abcc proteins in microcystin-LR (MCLR) transport, 1.135 μM MCLR was added to the bath or inside the sacs, in everted or non-everted preparations, respectively. Both luminal and serosal DNP-SG efflux were significantly inhibited by MCLR. A concentration-response curve obtained using strips from middle intestine yielded an IC50 value of 1.33 μM MCLR. The Abcc inhibitor, MK571 produced concentration-dependent inhibition of DNP-SG similar to that produced by MCLR. Since competition of MCLR and CDNB as GST substrates could bias the DNP-SG transport results, we evaluated the effects of MCLR on calcein efflux, which does not depend on GST activity. We applied the non-fluorescent, cell-permeant compound calcein-AM (0.25 μM) to middle intestinal strips and recorded the efflux of its hydrolysis product, the fluorescent Abcc substrate calcein. 2.27 μM MCLR and 3 μM MK571 inhibited calcein efflux (17.39 and 20.2%, respectively). Finally, MCLR interaction with Abcc transporters was evaluated by measuring its toxic intracellular effects. Middle intestinal segments were incubated in saline solution with 1.135 μM MCLR (MC1), 2.27 μM MCLR (MC2), 3 μM MK571 (MK) or 1.135 μM MCLR+3 μM MK571 (MC1/MK). After 1h, GSH concentration, protein phosphatase 1 and 2A (PP1, PP2A) and GST activities were measured in each segment. MC1did not produce significant effect while MC1/MK and MC2 significantly inhibited PP1and PP2A in similar proportions (34-49%). MK alone significantly increased PP2A activity (40%) with no effect in any other variable. GST activity and GSH concentration were not affected by any treatment. Concentration-response curves for MCLR (1.135 to 13.62 μM) alone or plus 3 or 6 μM MK571 were obtained using PP1 activity as response variable. The IC50 values were 1.0, 0.52, and 0.37 μM, respectively. Our results suggest that O. mykiss enterocytes are capable of eliminating MCLR by GST-mediated conjugation and luminal excretion through an Abcc-like apical transporter. This mechanism would prevent toxic effects and reduce the toxin uptake into the blood, which is likely mediated by basolateral Abccs.

NF-κB plays a key role in microcystin-RR-induced HeLa cell proliferation and apoptosis

Microcystins (MCs) are well-known cyanobacterial toxins produced in eutrophic waters and can act as potential carcinogens and have caused serious risk to human health. However, pleiotropic even paradoxical actions of cells exposure to MCs have been reported, and the mechanisms of MC-induced tumorigenesis and apoptosis are still unknown. In this study, we performed the first comprehensive in vitro investigation on carcinogenesis associated with nuclear factor kappa B (NF-κB) and its downstream genes in HeLa cells (Human cervix adenocarcinoma cell line from epithelial cells) exposure to MC-RR. HeLa cells were treated with 0, 20, 40, 60, and 80 µg/mL MC-RR for 4, 8, 12, and 24 h. HeLa cells presented dualistic responses to different doses of MCs. CCK8 assay showed that MC-RR exposure evidently enhanced cell viability of HeLa cells at lower MCs doses. Cell cycle and apoptosis analysis revealed that lower MCs doses promoted G1/S transition and cell proliferation while higher doses of MCs induced apoptosis, with a dose-dependent manner. Electrophoretic mobility shift assay (EMSA) revealed that MC-RR could increase/decrease NF-κB activity at lower/higher MC-RR doses, respectively. Furthermore, the expression of NF-κB downstream target genes including c-FLIP, cyclinD1, c-myc, and c-IAP2 showed the same variation trend as NF-κB activity both at mRNA and protein levels, which were induced by lower doses of MC-RR and suppressed by higher doses. Our data verified for the first time that NF-κB pathway may mediate MC-induced cell proliferation and apoptosis and provided a better understanding of the molecular mechanism for potential carcinogenicity of MC-RR.

Effects of the amino acid constituents of microcystin variants on cytotoxicity to primary cultured rat hepatocytes

Microcystins, which are cyclic heptapeptides produced by some cyanobacterial species from algal blooms, strongly inhibit serine/threonine protein phosphatase and are known as hepatotoxins. Microcystins have many structural variations, yet insufficient information is available on the differences in the cytotoxic potentials among the structural variants. In this study, the cytotoxicities of 16 microcystin variants at concentrations of 0.03–10 μg/mL to primary cultured rat hepatocytes were determined by measuring cellular ATP content, and subsequently determined by their 50% inhibitory concentration (IC₅₀). Differences in the amino acid constituents were associated with differences in cytotoxic potential. [d-Asp³, Z-Dhb⁷] microcystin-LR exhibited the strongest cytotoxicity at IC₅₀ of 0.053 μg/mL among the microcystin variants tested. Furthermore, [d-Asp³, Z-Dhb⁷] microcystin-HtyR was also highly cytotoxic. These results suggest that both d-Asp and Z-Dhb residues are important in determining the cytotoxic potential of microcystin variants.

Toxicological evaluation of microcystins in aquatic fish species: current knowledge and future directions

Microcystins (MCs) are algal toxins produced intracellularly within the algal cells, and are subsequently released into the aquatic systems. An increase in the frequency and intensity of occurrence of harmful algal blooms has directed the global attention towards the presence of MCs in aquatic systems. The effects of MCs on fish have been verified in a number of studies including histological, biochemical and behavioral effects. The toxicological effects of MCs on different organs of fish are related to the exposure route (intraperitoneal injection, feeding or immersion), the mode of uptake (passive or active transport) as well as biotransformation and bioaccumulation capabilities by different organs. This paper reviews the rapidly expanding literature on the toxicological evaluation of MCs in fish from both field studies and controlled laboratory experimental investigations, integrates the current knowledge available about the mechanisms involved in MC-induced effects on fish, and points out future research directions from a cross-disciplinary perspective. In addition, the need to carry out systematic fish toxicity studies to account for possible interactions between MCs and other environmental pollutants in aquatic systems is discussed.

Accumulation and biochemical effects of microcystin-LR on the Patagonian pejerrey (Odontesthes hatcheri) fed with the toxic cyanobacteria Microcystis aeruginosa

We studied accumulation and biochemical effects of microcystin-LR (MCLR) in Odontesthes hatcheri after dietary administration of the cyanobacteria Microcystis aeruginosa (1.3 μg MCLR/g body mass, incorporated in standard fish food). After 12 h, MCLR content in liver did not differ between fish fed with crushed or intact cells, demonstrating O. hatcheri's capacity to digest cyanobacteria and absorb MCLR. In the second experiment, fish received toxic cells, non-toxic cells, or control food; MCLR accumulation was monitored for 48 h. Protein phosphatase 1 (PP1), catalase (CAT), glutathione-S-transferase (GST) activities, and lipid peroxidation (as MDA) were measured in liver and intestine. Methanol-extractable MCLR was determined by PP1 inhibition assay (PPIA); extractable and protein-bound MCLR were measured by Lemieux oxidation-gas chromatography/mass spectrometry (GC/MS). MCLR accumulated rapidly up to 22.9 and 9.4 μg MCLR/g in intestine and liver, respectively, followed by a decreasing tendency. Protein-bound MCLR represented 66 to ca. 100 % of total MCLR in both tissues. PP1 activity remained unchanged in intestine but was increased in liver of MCLR treated fish.CAT and GST activities and MDA content were significantly increased by MCLR only in liver. We conclude that O. hatcheri is able to digest cyanobacteria, accumulating MCLR mostly bound to proteins. Our data suggest that this freshwater fish can be adversely affected by cyanobacterial blooms. However, the rapid decrease of the detectable MCLR in both tissues could imply that sublethal toxin accumulation is rapidly reversed.

Oxidative damage and apoptosis induced by microcystin-LR in the liver of Rana nigromaculata in vivo

Microcystins (MCs) are hepatotoxins with potent inhibitor activity of protein phosphatases PP1 and PP2A. The present study shows that MC-LR can induce severe oxidative damage and apoptosis in the livers of frogs (Rana nigromaculata) exposed to 1μg/L MC-LR for 7 and 14d in vivo. Ultrastructural observation showed the apoptotic morphology of perinuclear chromatin margination and swollen mitochondria, indicating that MC-LR can significantly damage frog liver. Reactive oxygen species (ROS) production and malondialdehyde (MDA) content were positively correlated with exposure time. Meanwhile, reduced glutathione (GSH) content and GSH peroxidase (GPx) activity rapidly decreased after prolonged exposure to 1μg/L MC-LR in a time-dependent manner. These results imply that the antioxidant defense systems of the liver were damaged. Enhanced apoptosis of cells in the livers of MC-treated frogs was detected by terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end labeling (TUNEL) associated with up-regulation of the mitochondrial system. MC-LR significantly stimulated the livers to release cytochrome c, which improved the protein expressions of Bax, caspase-3, and caspase-9 (p<0.01) and inhibited the protein expression of Bcl-2 with prolonged exposure (p<0.01) via the mitochondrial pathway. These results imply that the mitochondrial pathway has a key function in toxin-induced liver cell apoptosis. The expression of caspase-8 was induced significantly (p<0.01), which illustrates the mechanism that the death receptor pathway is also involved in apoptosis. The present findings show that MC-LR can induce apoptosis in frog liver, which may be related with the decline of amphibian populations. The World Health Organization-recommended drinking water limit for MC-LR in water may be not safe for amphibians.

Microcystins in potable surface waters: toxic effects and removal strategies

In freshwater, harmful cyanobacterial blooms threaten to increase with global climate change and eutrophication of surface waters. In addition to the burden and necessity of removal of algal material during water treatment processes, bloom-forming cyanobacteria can produce a class of remarkably stable toxins, microcystins, difficult to remove from drinking water sources. A number of animal intoxications over the past 20 years have served as sentinels for widespread risk presented by microcystins. Cyanobacterial blooms have the potential to threaten severely both public health and the regional economy of affected communities, particularly those with limited infrastructure or resources. Our main objectives were to assess whether existing water treatment infrastructure provides sufficient protection against microcystin exposure, identify available options feasible to implement in resource-limited communities in bloom scenarios and to identify strategies for improved solutions. Finally, interventions at the watershed level aimed at bloom prevention and risk reduction for entry into potable water sources were outlined. We evaluated primary studies, reviews and reports for treatment options for microcystins in surface waters, potable water sources and treatment plants. Because of the difficulty of removal of microcystins, prevention is ideal; once in the public water supply, the coarse removal of cyanobacterial cells combined with secondary carbon filtration of dissolved toxins currently provides the greatest potential for protection of public health. Options for point of use filtration must be optimized to provide affordable and adequate protection for affected communities.

Microcystin-LR inhibited hippocampal long-term potential via regulation of the glycogen synthase kinase-3β pathway

We previously demonstrated that Cyanobacteria-derived microcystin-LR (MCLR) is able to induce cognitive dysfunction, but the mechanism is not understood. Long-term potential (LTP) in hippocampus is regarded as an important cellular mechanism of learning and memory. Here, the aim of this study was to evaluate the role of MCLR in LTP of hippocampal dentate gyrus (DG) by in vivo electrophysiological recording. We found that MCLR could suppress the induction of LTP in rat hippocampus, whereas simultaneous inhibition of glycogen synthase kinase-3β (GSK-3β) by LiCl or SB216763 attenuated the LTP impairments by MCLR. Furthermore, a decrease of the phosphorylated level at Ser9 of GSK-3β was observed by western blotting after intracerebroventricular (ICV) injection of MCLR, indicating GSK-3β was activated by MCLR. In addition, we showed that ICV administration of MCLR slightly stimulated activity of protein phosphatases (PPs) in the brain, which might activate GSK-3β via dephosphorylation of Ser9 site. Taken together, these findings demonstrated that GSK-3β plays a crucial role in regulating MCLR-induced cognitive deficit.

Artificially-born "killer" lake: phytoplankton based water quality and microcystin affected fish in a reconstructed lake

Lake Karla (Greece) is an example of a lake ecosystem which was dried in 1960's and now is restored, facing various anthropogenic pressures, whereas it is also listed in the network of Greek protected areas in terms of its conservation value. The objective of the present study was to determine the presence of microcystins (MCYST) in the lake water and their accumulation in tissues of the commercial fish species Cyprinus carpio, along with the highlighting of phytoplankton community and general limnological features of Lake Karla, a newly reconstructed lake, the first year of its refilling. MCYST concentrations in water and fish tissues were determined by an enzyme-linked immunosorbent assay (ELISA). Results suggest that Lake Karla has undergone a progressive cultural eutrophication with frequent cyanobacterial blooms. The most dominant species in lake's phytoplankton were Anabaenopsis elenkinii, Sphaerospermopsis and Planktothrix agardhii. MCYST concentrations were detected in water samples comparable to those reported for other eutrophicated Mediterranean lakes while considerable amounts of MCYST were detected in the tissues of the species C. carpio in the following order: liver>kidney>brain>intestine>muscles. The presence of prominent cyanobacterial blooms dominated by toxic species highlights the need to undertake eutrophication control measures so as to avoid further toxicological problems.

Identification of apoptosis-related genes and transcription variations in response to microcystin-LR in zebrafish liver

There is growing evidence that the effects of microcystin-LR (MC-LR) are closely related to apoptosis. This study utilized microarray to identify the apoptosis-related genes induced by MC-LR in zebrafish liver. The messenger RNA abundance of some apoptosis-related genes was found to be increased, including five tumor necrosis factor (TNF)-related members (apoptosis regulatory protein siva, tumor necrosis factor-α (tnfa) TNF (ligand) superfamily member 10 (tnfsf10), TNF-inducible protein 6 (tnfaip6) and TNF receptor associated factor 2 binding protein (traf2bp)), three p53-related genes (tumor protein p53 inducible nuclear protein 1 (tp53inp1), p53-induced protein phosphatase 1 (ppm1d) and a novel apoptosis stimulating protein of p53 (aspp2)), bcl 2 family members (proapoptosis gene bax and antiapoptosis gene mcl 1), caspases (caspase y (caspy) and a PYD and CARD domain-containing protein (pycard)) and the transforming growth factor beta (TGF-β) induced apoptosis protein 2 (taip2). Real-time polymerase chain reaction was used to study the kinetic transcriptional changes in seven apoptosis-related genes. Elevated transcription of p53, tp53inp1, mcl 1 and taip2 could only be detected at 6 h, increased transcription of the antagonist molecules, bcl 2 and bax could be detected at most time points and the significant change of caspy could be found at 48 h and 72 h after stimulation. Taken together, the results obtained in the present study clearly demonstrate that large amount of apoptosis-related genes are involved in the regulation of MC-LR-induced apoptosis.

Involvement of endoplasmic reticulum and autophagy in microcystin-LR toxicity in Vero-E6 and HepG2 cell lines

This work investigates the involvement of the endoplasmic reticulum (ER) and autophagy in microcystin-LR (MCLR) toxicity in Vero-E6 and HepG2 cell lines. Additionally, morphological alterations induced by MCLR in lysosomes and mitochondria were studied. Cytotoxicity evaluation showed that pure MCLR and MCLR from LMECYA110 extract induce concentration dependent viability decays after 24h exposure. HepG2 cells showed an increased sensitivity to MCLR than Vero cells, with lower cytotoxic thresholds and EC(50) values. Conversely, LC3B immunofluorescence showed that autophagy is triggered in both cell lines as a survival response to low MCLR concentrations. Furthermore, MCLR induced a MCLR concentration-dependent decrease of GRP94 expression in HepG2 cells while in Vero cells no alteration was observed. This suggests the involvement of the ER in HepG2 apoptosis elicited by MCLR, while in Vero cells ER destructuration could be a consequence of cytoskeleton inflicted damages. Additionally, in both cell lines, lysosomal destabilization preceded mitochondrial impairment which occurred at high toxin concentrations. Although not an early cellular target of MCLR, mitochondria appears to serve as central mediators of different signaling pathways elicited by the organelles involved in MCLR toxicity. As a result, kidney and hepatic cell lines exhibit cell type and dose-dependent mechanisms to overcome MCLR toxicity.

Assessment of microcystin distribution and biomagnification in tissues of aquatic food web compartments from a shallow lake and evaluation of potential risks to public health

The objectives of this study were: (1) to examine the distribution and bioaccumulation of microcystins in the main components of the food web (phytoplankton, zooplankton, crayfish, shrimp, mussel, snail, fish, frog) of Lake Pamvotis (NW Greece), (2) to investigate the possibility of microcystin biomagnification and (3) to evaluate the potential threat of the contaminated aquatic organisms to human health. Significant microcystin concentrations were detected in all the aquatic organisms during two different periods, with the higher concentrations observed in phytoplankton and the lower in fish species and frogs. This is the first study reporting microcystin accumulation in the body of the freshwater shrimp Atyaephyra desmsaresti, in the brain of the fish species common carp (Cyprinus carpio) and in the skin of the frog Rana epirotica. Although there was no evidence for microcystin biomagnification, the fact that microcystins were found in lake water and in the tissues of aquatic organisms, suggests that serious risks to animal and public health are possible to occur. In addition, it is likely to be unsafe to consume aquatic species harvested in Lake Pamvotis due to the high-concentrations of accumulated microcystins.

Mature hepatocytes exhibit unexpected plasticity by direct dedifferentiation into liver progenitor cells in culture

Although there have been numerous reports describing the isolation of liver progenitor cells from the adult liver, their exact origin has not been clearly defined; and the role played by mature hepatocytes as direct contributors to the hepatic progenitor cell pool has remained largely unknown. Here, we report strong evidence that mature hepatocytes in culture have the capacity to dedifferentiate into a population of adult liver progenitors without genetic or epigenetic manipulations. By using highly purified mature hepatocytes, which were obtained from untreated, healthy rat liver and labeled with fluorescent dye PKH2, we found that hepatocytes in culture gave rise to a population of PKH2-positive liver progenitor cells. These cells, liver-derived progenitor cells, which share phenotypic similarities with oval cells, were previously reported to be capable of forming mature hepatocytes, both in culture and in animals. Studies done at various time points during the course of dedifferentiation cultures revealed that hepatocytes rapidly transformed into liver progenitors within 1 week through a transient oval cell-like stage. This finding was supported by lineage-tracing studies involving double-transgenic AlbuminCreXRosa26 mice expressing β-galactosidase exclusively in hepatocytes. Cultures set up with hepatocytes obtained from these mice resulted in the generation of β-galactosidase-positive liver progenitor cells, demonstrating that they were a direct dedifferentiation product of mature hepatocytes. Additionally, these progenitors differentiated into hepatocytes in vivo when transplanted into rats that had undergone retrorsine pretreatment and partial hepatectomy.

CONCLUSION

Our studies provide strong evidence for the unexpected plasticity of mature hepatocytes to dedifferentiate into progenitor cells in culture, and this may potentially have a significant effect on the treatment of liver diseases requiring liver or hepatocyte transplantation.

The apoptotic effect of oral administration of microcystin-RR on mice liver

Microcystin produced by cyanobacteria in diverse water systems is a potent hepatotoxin that has been documented to induce hepatocyte apoptosis and liver injury. There are more than eighty reported microcystins. The present work aimed at investigating the apoptotic effect of MC-RR (a common member of microcystin family), and its related mechanism. MC-RR was administered orally to ICR mice for 7 days with different dosages. Apoptotic cell death in liver was detected by TUNEL assay, and the expression levels of Bcl-2, Bax and p53, GRP 78 and CHOP which have been reported to be related to apoptosis and ER stress were determined via western-blot. The activity of PP2A was measured using the serine-threonine phosphatase assay system and PP2A A subunit expression at both transcription and protein levels was measured by RT-PCR and western blot, respectively. A significant difference was observed on the number of TUNEL positive liver cells between the control and MC-RR-treated groups. The expression levels of Bcl-2, Bax, p53, and GRP 78 in MC-RR-treated groups were altered significantly compared to the control, but no obvious alteration was found in CHOP expression. The PP2A activity and A subunit expression did not manifest any obvious change at both transcription and protein levels. The results indicated that oral exposure to MC-RR can cause apoptosis as well as moderate ER stress in mice liver. The mitochondrial pathway via Bcl-2 family members may contribute to the apoptosis. However, PP2A may not be involved in the regulation of apoptotic process under the current conditions.

Pathological modifications following sub-chronic exposure of medaka fish (Oryzias latipes) to microcystin-LR

Microcystins (MCs) are toxic monocyclic heptapeptides produced by many cyanobacteria. MCs, especially MC-LR, cause toxic effects in animals and are a recognized potent cause of environmental stress and health hazard in aquatic ecosystems when heavy blooms of cyanobacteria appear. Consequently, one of the major problems is the chronic exposure of fish to cyanotoxins in their natural environment. The present experiment involving chronic exposure confirmed initial findings on acute exposure to MC contamination: exacerbated physiological stress and tissue damage in several tissues of exposed medaka fish. The gonads were affected specifically. In female gonads the modifications included reduction of the vitellus storage, lysis of the gonadosomatic tissue and disruption of the relationships between the follicular cells and the oocytes. In the males, spermatogenesis appeared to be disrupted. This is the first report showing that a cyanotoxin can affect reproductive function, and so can impact on fish reproduction and thus fish stocks.

Oral toxicity of extracts of the microcystin-containing cyanobacterium Planktothrix agardhii to the medaka fish (Oryzias latipes)

As previously demonstrated the medaka fish appears to offer a good model for studies of microcystins (MCs) effects. Since cyanobacterial toxins are released with other molecules in the aquatic environment when the producers are dying, in this study, we performed additional experiments in order to compare the described effects obtained with the pure toxin microcystin-LR (MC-LR), among the most toxic MCs, to those induced by complex extracts of an MCs-producer Planktothrix agardhii, strain PMC 75.02 and a natural bloom containing the MCs-producer P. agardhii. The toxicity of these extracts containing several variants of MC was determined in adult medaka treated by gavage. Extracts of an MCs-free strain of P. agardhii (PMC 87.02) were assayed for comparison. Extracts effects were analysed on two tissues, liver and intestine by means of photon and transmission electron microscopy. MC was localized in these tissues by immunocytochemistry. No effect was detectable with extracts of the MCs-free P. agardhii strain. The two MCs-P. agardhii extracts (strain and natural bloom) were able to induce harmful effects in the liver and intestine of the medaka fish in acute intoxication by gavage. In these target organs as shown by toxin immunolocalization, reactions leading to cell disjunction and lysis were observed apparently associated with an immune reaction implying MC containing macrophages. These effects are similar to those previously described with photonic microscopy in medaka treated with pure MC-LR with additional results obtained under the electron microscope. Since no significant effect was detected with the MCs-free (PMC 87.02) extract, we then conclude that MCs, even in complex association with other cyanobacterial components, should be responsible for the toxic effects observed in treated fish.

Antioxidant response in liver of the phytoplanktivorous bighead carp (Aristichthys nobilis) intraperitoneally-injected with extracted microcystins

The worldwide occurrence of cyanobacterial blooms makes it necessary to perform environmental risk assessment procedures to monitor the effects of microcystins (MCs) on fish. Oxidative stress biomarkers are valuable tools in this regard. In the present study, phytoplanktivorous bighead carp (Aristichthys nobilis) were injected intraperitoneally (i.p.) with extracted MCs (mainly MC-RR and -LR) at two doses, 400 and 1,000 microg kg(-1) bw, and antioxidant responses of the liver as biomarkers of oxygen-mediated toxicity were studied at 1, 3, 12, 24 and 48 h after injection. Contents of reactive oxygen species (ROS) and activities of antioxidant enzymes [catalase (CAT), superoxide dismutase (SOD), glutathione peroxide (GPX), and glutathione reductase (GR)] as well as glutathione S-transferase (GST) in the liver in both dose groups showed a biphasic change with an increase at initial 3 h followed by a decrease after injection, owing to the roles of the antioxidant system in eliminating excessive ROS and regenerating glutathione (GSH). The increased GST was probably due to the high transcription of cytosolic GST alpha and rho, suggesting the importance of MCs detoxification by GSH pathway. The stable GSH levels in liver may be explained by the high basic GSH concentration in liver, and/or an increased GSH synthesis, suggesting a high ability to detoxify MCs and to release associated high oxidative pressure in phytoplantivorous fish.

Cyanobacterial cyclopeptides as lead compounds to novel targeted cancer drugs

Cyanobacterial cyclopeptides, including microcystins and nodularins, are considered a health hazard to humans due to the possible toxic effects of high consumption. From a pharmacological standpoint, microcystins are stable hydrophilic cyclic heptapeptides with a potential to cause cellular damage following uptake via organic anion-transporting polypeptides (OATP). Their intracellular biological effects involve inhibition of catalytic subunits of protein phosphatase 1 (PP1) and PP2, glutathione depletion and generation of reactive oxygen species (ROS). Interestingly, certain OATPs are prominently expressed in cancers as compared to normal tissues, qualifying MC as potential candidates for cancer drug development. In the era of targeted cancer therapy, cyanotoxins comprise a rich source of natural cytotoxic compounds with a potential to target cancers expressing specific uptake transporters. Moreover, their structure offers opportunities for combinatorial engineering to enhance the therapeutic index and resolve organ-specific toxicity issues. In this article, we revisit cyanobacterial cyclopeptides as potential novel targets for anticancer drugs by summarizing existing biomedical evidence, presenting structure-activity data and discussing developmental perspectives.

Molecular aspects of microcystin-induced hepatotoxicity and hepatocarcinogenesis

It is known that microcystin (MC) is a cyanotoxin that is a potent environmental inhibitor of eucariotic protein serine/threonine phosphatase 1 and 2A, both in vitro and in vivo. Consequently, these cyanobacterial toxins (MC-IARC group 2B carcinogen, MC extracts-group 3) are potent tumor promoters and there is an indication that they may also act as tumor initiators. The ability of microcystin-LR (MC-LR) to act as a tumor initiator is based on fact that it can induce DNA damage either by direct interaction with DNA or by indirect mechanisms through formation of reactive oxygen species (ROS). Both acute and chronic exposures, to either low or high doses of MC-LR, can activate apoptotic pathways. Chronic exposure to low concentrations of MC-LR contributes to increased risk for cancer development. Epidemiological studies, in certain areas of China, have suggested that MC is one of the risk factors for the high incidence of primary liver cancer (PLC). Recently, we have reported a correlation between PLC and cyanobacterial "blooms" in reservoirs used as a source for drinking water supply in central Serbia. It appears that the combination of acute and chronic exposures to both high and low doses of MC can lead to PLC initiation and promotion. Based on this, we propose that the requirement for the co-factors such as aflatoxin B1 and other mycotoxins, HBV, HCV, alcohol, etc. is not needed for initiation and promotion of PLC by MC-LR as was suggested earlier. The possible mechanisms of the genotoxicity of MC and its role as a hepatocarcinogen are outlined in this review. Furthermore, we show that the exposure of hepatocytes to MC can lead either to malignant proliferation or apoptosis.

Cyanotoxins from black band disease of corals and from other coral reef environments

Many cyanobacteria produce cyanotoxins, which has been well documented from freshwater environments but not investigated to the same extent in marine environments. Cyanobacteria are an obligate component of the polymicrobial disease of corals known as black band disease (BBD). Cyanotoxins were previously shown to be present in field samples of BBD and in a limited number of BBD cyanobacterial cultures. These toxins were suggested as one of the mechanisms contributing to BBD-associated coral tissue lysis and death. In this work, we tested nine cyanobacterial isolates from BBD and additionally nine isolated from non-BBD marine sources for their ability to produce toxins. The presence of toxins was determined using cell extracts of laboratory grown cyanobacterial cultures using ELISA and the PP2A assay. Based on these tests, it was shown that cyanobacterial toxins belonging to the microcystin/nodularin group were produced by cyanobacteria originating from both BBD and non-BBD sources. Several environmental factors that can be encountered in the highly dynamic microenvironment of BBD were tested for their effect on both cyanobacterial growth yield and rate of toxin production using two of the BBD isolates of the genera Leptolyngbya and Geitlerinema. While toxin production was the highest under mixotrophic conditions (light and glucose) for the Leptolyngbya isolate, it was highest under photoautotrophic conditions for the Geitlerinema isolate. Our results show that toxin production among marine cyanobacteria is more widespread than previously documented, and we present data showing three marine cyanobacterial genera (Phormidium, Pseudanabaena, and Spirulina) are newly identified as cyanotoxin producers. We also show that cyanotoxin production by BBD cyanobacteria can be affected by environmental factors that are present in the microenvironment associated with this coral disease.

Localization of microcystin-LR in medaka fish tissues after cyanotoxin gavage

Microcystins (MCs) are toxic monocyclic heptapeptides produced by many cyanobacteria. Over 70 MCs have been successfully isolated and identified, of which MC-LR is the most commonly occurring toxin. Microcystins, especially MC-LR, cause toxic effects in mammals, birds and fish and are a recognized potent cause of environmental stress and pose a potential health hazard in aquatic ecosystems when heavy blooms of cyanobacteria appear. They also constitute a public health threat to people via drinking water and food chains. The concentrations of MC-LR can be very low, even in fish displaying severely disrupted tissues, which makes it essential to devise selective and sensitive histochemical methods for identifying and localizing MC-LR in target organs, such as liver and intestine. The aim of the study reported here was to analyze the presence of MC-LR in contaminated fish tissues using immunohistochemical methods. The present experiment involving subacute exposure confirmed our initial hypothesis that subacute and acute exposure to microcystin contamination can exacerbate physiological stress, induce sustained pathological damage, and affect the immune response in exposed medaka fish.

Acyloxymethyl esterification of nodularin-R and microcystin-LA produces inactive protoxins that become reactivated and produce apoptosis inside intact cells

We report the esterification of the carboxyl groups of the cyclic peptide toxins nodularin-R and microcystin-LA to produce stable diacetoxymethyl and dipropionyloxymethyl ester derivatives. The derivatives had no activity but were reactivated upon esterase treatment. When injected into cells, the acyloxymethyl moieties were cleaved off and apoptosis induced. Linking the acyloxymethyl-ester moiety of these potent toxins to carriers destined for endocytosis paves the way for selective apoptosis induction in target (e.g., cancer) cells.

Comparative study of cyanotoxins affecting cytoskeletal and chromatin structures in CHO-K1 cells

In this study we compared the effects of the two frequently occuring and most dangerous cyanobacterial toxins on the cellular organization of microfilaments, microtubules and on the chromatin structure in Chinese hamster ovary (CHO-K1) cells. These compounds are the widely known microcystin-LR (MC-LR) and cylindrospermopsin (CYN) classified as the highest-priority cyanotoxin. Toxic effects were tested in a concentration and time dependent manner. The hepatotoxic MC-LR did not cause significant cytotoxicity on CHO-K1 cells under 20 microM, but caused apoptotic changes at higher concentrations. Apoptotic shrinkage was associated with the shortening and loss of actin filaments and with a concentration dependent depolymerization of microtubules. No necrosis was observed over the concentration range (1-50 microM MC-LR) tested. Cylindrospermopsin did cause apoptosis at low concentrations (1-2 microM) and over short exposure periods (12h). Necrosis was observed at higher concentrations (5-10 microM) and following longer exposure periods (24 or 48h). Cyanotoxins also affected the chromatin structure. The condensation process was inhibited by MC-LR at a later stage and manifested as broken elongated prechromosomes. CYN inhibited chromatin condensation at the early fibrillary stage leading to blurred fluorescent images of apoptotic bodies and preventing the formation of metaphase chromosomes. Cylindrospermopsin exhibited a more pronounced toxic effect causing cytoskeletal and nuclear changes as well as apoptotic and necrotic alterations.

Protective efficacy of the antioxidants vitamin E and Trolox against Microcystis aeruginosa and microcystin-LR in Artemia franciscana nauplii

This study was undertaken to evaluate the protective efficacy of the antioxidants vitamin E and Trolox (a water-soluble vitamin E derivative) against the toxicity of microcystin-LR (MC-LR), Microcystis aeruginosa aqueous extract (CE), and a reference toxin, menadione sodium bisulfite (MSB), in Artemia franciscana nauplii. This was achieved by using the well-established brine shrimp bioassay. The experiment was conducted in 2 stages, with (1) 12-h mortality time course and (2) LC50 determination for 12- and 24-h exposures. Treatments consisted of MC-LR, CE, and MSB alone and with 4-h pretreatments of either vitamin E or Trolox. Sensitivity of A. franciscana nauplii with 24-h LC50 values of 11 (10.1-12.1) microg/ml for MSB and 9.5 (8.8-10.4) microg/ml for MC-LR were in general agreement with values reported for Artemia sp. Both antioxidant pretreatments resulted in significant reductions in mortality of approximately 50% at 9 h postexposure when challenged by either 40 microg/ml MC-LR or 20 microg/ml MSB. In contrast, the antioxidant pretreatments offered little to no protection from CE, suggesting that other uncharacterized bioactive compounds contributed to overall toxicity. The described bioassay is easily accessible, inexpensive, rapid, and complies with animal ethics guidelines of many countries, and thus provides a potential alternative to the mouse bioassay for the initial screening for chemoprotectants against MC-LR toxicity.

Hepatoprotective efficacy of certain flavonoids against microcystin induced toxicity in mice

Toxic cyanobacteria (blue-green algae) water blooms have become a serious problem in several industrialized areas of the world. Microcystin-LR (MC-LR) is a cyanobacterial heptapeptide that represents acute and chronic hazards to animal and human health. Identification of suitable chemprotectants against microcystin is essential considering human health hazards. In the present study, we have evaluated the protective efficacy of three flavanoids namely quercetin (200 mg/kg), silybin (400 mg/kg), and morin (400 mg/kg)] pretreatment against microcystin toxicity (0.75 LD(50), 57.5 microg/kg) in mice. Various biochemical variables were measured to study the recovery profile of protected animals at 1- and 3-days post-toxin treatment. The serum alanine amino transferase (ALT) shows 17-fold increase in MC-LR treated animals compared with control group at 1 day. The silybin and quercetin group showed a decrease in level of ALT compared with MC-LR group but still higher than control group. No significant protection was observed with aspartate aminotransaminase (AST) and lactate dehydrogenase (LDH) levels in flavanoid-treated groups at 1-day post-treatment. But at 3 days, the serum levels of AST and ALT were normalized to control values, but the serum LDH levels were still significantly higher than the control group. No significant changes were observed in glutathione peroxidase and reduced glutathione levels at both 1- and 3-day postexposure. The catalase activity shows a significant decrease in quercetin-treated animals at 3-day postexposure. The protein phosphatase was significantly inhibited in MC-LR group compared to control. The silybin pretreated group showed recovery after 1 day. At 3 days, the PPAse activity was reversed to control values in all the flavanoid-treated groups. Immunoblotting analysis showed microcystin-PPAse adduct in liver tissues of toxin-treated as well as flavanoid-treated mice even after 3 days. The results of this study show that flavanoids, quercetin, silybin, and morin could reverse the hepatotoxic effects of MC-LR in vivo.